The present invention generally relates to a locking system. More specifically, the present invention relates to a locking system for positioning one component in linear spaced relation relative to another component by way of conventional rotational threading, wherein when used with orthopedic implants, such spaced relation may linearly and/or eccentrically position one implant component (e.g., a tibial stem) relative to another implant component (e.g., a tibial baseplate).
Locking systems for positioning one implant component in spaced relation relative to another implant component are generally known in the art, and may be used to adjust the vertical and/or angular positioning of an implantable tibial stem or the like relative to an implantable tibial baseplate or the like. But, such systems known in the art use non-conventional rotational threading. For example, FIGS. 1-6 illustrate a tibial implant 30 having a prior art locking system 32 designed to couple a tibial stem extension 34 relative to a corresponding tibial baseplate 36. More specifically, the prior art locking system 32 includes an angled extension 38 that threadingly engages the tibial stem extension 34 on one end (threads not shown) and threadingly engages the tibial baseplate 36 on the other end by way of a threaded section 39. The threaded section 39 may include a first set of exterior threads 40 (FIGS. 2, 4, and 5) that threadingly engage a series of interior threads within the tibial baseplate 36 and a second set of oppositely threaded exterior threads 41 (FIGS. 2, 5, and 6) that threadingly engage a set of internal threads (not shown) of a locknut 42.
In operation, each of the tibial stem extension 34, the angled extension 38, the locknut 42, and the tibial baseplate 36 are screwed together into the configuration shown in FIG. 3. In this example, rotating the tibial stem extension 34 along the rotational arrow A in FIG. 3 tightens threaded engagement of the tibial stem extension 34 with the angled extension 38, and opposite rotation loosens the threaded engagement therewith. The same is true for threaded engagement of the angled extension 38 with the tibial baseplate 36, i.e., rotating the angled extension 38 along the rotational arrow B in FIG. 3 causes the angled extension 38 to threadingly engage the tibial baseplate 36 along the first set of exterior threads 40, while opposite rotation loosens or disengages the angled extension 38 with respect to the tibial baseplate 36 along the first set of exterior threads 40. The locknut 42 is threaded for engagement with the second set of exterior threads 41, which are oppositely threaded the first set of exterior threads 40. More specifically, in this embodiment, the rotational movement of the locknut 42 along rotational arrow C causes threaded engagement with the angled extension 38 (i.e., the locknut 42 moves along the threads away from the tibial baseplate 36 and toward the angled extension 38 in FIG. 3), while opposite rotation causes the locknut 42 to disengage the angled extension 38 (i.e., the locknut 42 moves along the threads toward the tibial baseplate 36 and away from the angled extension 38 in FIG. 3). When the angled extension 38 and the locknut 42 are rotated commonly along the direction of the rotational arrows B and C, both move in opposite directions. That is, the angled extension 38 threadingly engages the tibial baseplate 36 and the locknut 42 threadingly engages the angled extension 38 and moves away from the tibial baseplate 36. The drawback of this structure is that common rotational movement of the angled extension 38 and the locknut 42 in the direction of rotational of arrows B and C brings the two components together. This inhibits desired locking engagement between the locknut 42 and the tibial baseplate 36. As such, it can be difficult to properly tighten the prior art locking system 32. In this respect, the opposite rotational operation of the locknut 42 is counterintuitive and can be confusing and particularly frustrating during surgery.
To extend the distance between the tibial stem extension 34 and the tibial baseplate 36, the angled extension 38 is unscrewed from the tibial baseplate 36 by some desired distance 44, e.g., as shown in FIG. 4, by way of rotating the angled extension 38 along the rotational arrow B′ (FIG. 4) relative to the tibial baseplate 36. The desired distance 44 may be the result of the desired vertical displacement of the tibial stem extension 34 relative to the tibial baseplate 36, or the desired angular positioning of the tibial stem extension 34 by way of being coupled to the angled extension 38. In the position shown in FIG. 4, the first set of exterior threads 40 are re-exposed as a result of backing off (unscrewing) the angled extension 38 from the tibial baseplate 36. Once the desired distance 44 is attained, the tibial stem extension 34 must be locked in place relative to the tibial baseplate 36. This is accomplished by rotating the locknut 42 along rotational arrow C′ (FIG. 5) along the exterior threads 40, which causes the locknut 42 to move away from the body of the angled extension 38 and toward the tibial baseplate 36. This is counter-intuitive to conventional threading. In this respect, the locknut 42 is basically tightened up against the tibial baseplate 36 while the tibial stem extension 34 is held in place—FIG. 6 illustrates the locknut 42 engaged up underneath the tibial baseplate 36 in this respect. Hand-tightening the locknut 42 up underneath the tibial baseplate 36 typically does not provide the desired tightening to prevent the locknut 42 from coming loose. Rather, once the locknut 42 is in the position shown in FIG. 6, further tightening is needed by way of rotation of the angled extension 38. This is accomplished by engaging the angled extension 38 with a first wrench or the like and engaging the locknut 42 with a second wrench or the like, then attempting to rotate each in opposite directions, i.e., generally rotating the angled extension 38 along directional arrow B (FIG. 3) to further engage the angled extension 38 with the tibial baseplate 36 and rotating the locknut 42 along rotational arrow C′ (FIG. 5) so the locknut 42 is forced to move away from the body of the angled extension 38 and into engagement with the tibial baseplate 36. Although, one problem with this prior art locking system 32 is that opposite rotation along rotational arrows B and C′ is counter-intuitive for the locknut 42, namely because it must be rotated opposite to convention to tighten.
There exists, therefore, a significant need in the art for a locking system that permits hand tightening of the locking system in the same or conventional rotational direction commonly associated with tightening a screw or nut to position one component in linear spaced relation relative to another component. The present invention fulfills these needs and provides further related advantages.